1. Field of the Invention
This invention relates to systems that are used for aligning a dental x-ray machine with an x-ray film plate.
2. Description of the Prior Art
Dental x-ray photography has become an invaluable diagnostic aid to the dentist and today is often routinely performed in the dental office. However, difficulties are encountered in obtaining proper alignment of the dental x-ray apparatus with an x-ray film plate because the film plate is positioned intraorally and therefore cannot be seen by the dentist or technician during the aiming process. To avoid the problem of misalignment, a larger x-ray beam size is often used. This assures that the complete film plate will be exposed; however, it also increases the hazard caused by the exposure of the patient to x-ray radiation.
Various x-ray alignment devices appear in the prior art which obtain proper positioning by mechanical means. U.S. Pat. No. 3,930,164 to Alexander discloses one such device that uses a centering rod to locate the center of the x-ray beam path and to position the subject accordingly. This particular device is used for x-rays of the temporo-mandibular joint. In U.S. Pat. No. 4,057,733 to Hofmockel discloses an x-ray image intensifier is mechanically mounted to the x-ray apparatus in such a manner that it can receive the emitted x-ray beam. The x-ray image received is reproduced on a video screen.
In German Offenlegungsschrift No. 2,134,106, to Graf there is disclosed an x-ray film plate which is positioned on a frame mounted to the x-ray apparatus.
These devices using mechanical mounting means to obtain alignment have several disadvantages in that they are uncomfortable to the patient; they are inconvenient to use and difficult to position within the mouth; they also pose a problem of sterilization. Further, the Alexander device is not adaptable for use in x-raying individual teeth within the mouth. The radioscopic device of Hofmockel involves expensive equipment. Because the Hofmockel device uses a continuous beam, the overall x-ray exposure to the patient is increased.
In the general field of x-ray alignment there are several devices which use optics in order to obtain the desired positioning. U.S. Pat. No. 4,060,733 to Franke discloses a light beam which is reflected to illuminate the area at which the x-ray machine is pointed. This is a convenient, simple aiming device however it is unsuitable to the field of dental x-rays, (because with dental x-rays neither the film position nor the teeth are typically exposed to view). U.S. Pat. No. 3,790,803 to Phillips dicloses another device that uses optics to obtain proper alignment. In Phillips a beam of light is emitted from a fixed position on the x-ray apparatus. The beam of light is reflected from a fixed position relative to the x-ray film plate. In this manner the device can indicate when there is proper alignment. U.S. Pat. No. 4,012,638 to Altschuler discloses a device which applies optics specifically to the field of dental x-ray alignment. In Altschuler a plurality of infrared emitters and detectors are positioned on the x-ray apparatus. The x-ray film plate is positioned on a frame which extends outside the mouth and has an infrared reflective surface. When the infrared light emitted is reflected back and detected then alignment is indicated. Altschuler possesses many of the disadvantages of the mechanically mounted alignment devices, in that the film plate frame necessarily has to extend outside of the mouth. This attribute presents the problems of discomfort to the patient and of difficulty in positioning the film plate in its desired location within the mouth. The Altschuler device has the further disadvantage in that it does not determine the distance between the x-ray apparatus and the x-ray film plate. This information is desirable to properly adjust the size of the x-ray beam and therefore limit the amount of x-ray exposure to the patient. This distance is typically fixed in the mechanically mounted devices.
The general area of dentistry has made use of magnets and Hall effect sensors in the past, though not in the field of x-ray alignment. U.S. Pat. No. 3,083,463 to Brooks, discloses a magnet is used in conjunction with a dental drill to produce an anesthetic effect. U.S. Pat. No. 3,839,797 to Randolph, discloses a dental drill paralleling system which uses a Hall effect sensor positioned in the field of a magnet where the magnetic field lines are substantially parallel. Proper alignment is indicated when the Hall effect sensor is parallel with the magnetic field lines.